1. Field of the Invention
This invention is related to a stable, reliable clock source for digital systems. More particularly, it is related to a clock source, comprising multiple oscillators, that continues to provide a stable clock signal if one of the oscillators fails.
2. Background Information
The various circuits of digital data processing systems operate in synchronization with a clock signal that is usually provided by a central (master) clock. Consequently if this clock fails, the entire system will fail. Attempts have been made to provide a master clock comprising multiple oscillators, where, if an oscillator fails, another oscillator will be switched in to provide the clock signal. However, this arrangement also leads to system failure because the switching causes an unacceptable phase change in the clock signal. Specifically, the system will fail if an edge in the master clock signal arrives either too soon or too late.
This invention is directed to the ability to provide a phase-stable clock signal even if one of the oscillators fails.